Drier



Nov. l, 1949 DRIER 4 Sheets-Sheet l wl r 1:/ n /N/ -7 4^ 7 MMAA/ w. m Nmm n, Sq ww man uw NN L N Sw .Wg

l N VEN TOR W/L L /A M MESs/A/GER ATTOENY Nov. l, 1949 W. MESSINGERDRIER Filed March 16, 1946 4 Sheets-Shea?l 2 ATTORNEY Nov.- l, 1949 w.`MEsslNcaER DRIER 4 Sheets-Sheet 5 Filed March 16, 1946 Nov. l, 1949 w.MEsslNsl-:R

DRIER 4 Sheets-Sheet 4 Filed March 16, 1946 INVEN TOR. lf//LL/AMMass/NGE@ Puentdlfv. 1,1949

UNI-TED s'rATEspPATENT oFFklcE This invention relates to dryers,particularly of the revolving cylinderv type. Such cylinders are adaptedto be heated internally, and the heat passing through the cylinder wallsis utilized for drying materials passing over the external surface ofthe cylinder, either in actual contact with the surface or on a beltpassing over the surface. Such a dryer is utilized in many arts forcontinuous drying of a variety of materials such as paper, chemicals andlms of liquid or viscous material;

Dryers of this type have given rise to serious problems and containinherent defects. In order to understand the nature of the problemswhich a designer of cylindrical dryers must face, the present practicewill be briefly outlined. Steam at 40 lbs/sq. in. is admitted into, thehollow interior oi the cylinder. A portion of the newly entering steam,meeting the large mass of steam and vapor which is at lower temperature,is condensed and produces a shower-like rain. This water falls to thebottom of the cylinder, but the speed of cylinder rotation is suilicientto carry the water in a layer completely around the circumference of theinterior wall of the cylinder.

Water is a relatively poor conductor of heat compared to steel or castiron-the usual metals of which dryer cylinders are formed. Further,water fed to evaporating boilers contains air which remains mixed withthe steam as it enters the dryer cylinder. In addition to an insulatinglayer of condensed vapor, there is formed an insulating layer of air.The air may form into pockets retarding heat transmission in specificspots to such degree as to generate what are known as cold spots on theexterior surface of the dryer cylinder.

One problem which has confronted the designer of such cylinders was toproduce a sufilciently high temperature within the cylinder s vthat inspite of the insulating layers of water and air on the interior surfaceof the cylinder the desired temperature of 220 to 280 F. wouldnevertheless be obtained on the exterior surface. The only solutionheretofore offered by the designers has been ever higher steam pressureswithin the cylinder, but this meant correspondingly increasing thicknessof cylinder wall. For example, in the paper industry, the Webs of'moistpaper issuing from the Fourdrinier are led to massive revolving dryerswhich may be 12 feet in diameter, 150 inch face width, with a wall 5inches thick, and weighing 180,000 pounds. In-

feated the benefits which were expected from 'cylinder wall.

6 Claims. (Cl. 34-124) the higher interior pressures and temperatures`since the rate of heat iiow is inversely proportional to the thicknessof metal traversed. The heat transfer in such thick-walled cylinders wasfurther cut down by the fact that such largediameter and thick-walleddryer cylinders are customarily not machined in the interior surface.Consequently there is present scale and oxide of the cast or rolled.metal which has a heat insulation value equivalent to several inchesthickness of metal.

By my invention I propose an entirely new method of designing such dryercylinders which abandons completely the unsatisfactory design procedureof increasing the steam pressure and. therefore, the cylinder wallthickness, in order to solve the problems created by the insulatingeffect of the layers of condensed vapor and air. It is one of theprincipal objects of this invention to provide a design of dryercylinder which will prevent the formation of such heatinsulating layersand thus obviate the necessity for high pressure steam and consequentthickening of the The reduction in weight is particularly important inthe paper industry where the dryer section may contain 50 to 150 dryercylinders. Not only can the size and weight of each cylinder be reducedby this invention, but the same drying effect can be obtained by asmaller number of cylinders. Reduction of pressure'will avoid the dangerinherent in excessively thick cylinder walls which crack from fatigueafter a few years service and may cause explosions because these dryerscontain tons of water of condensation above the boiling temperature andunder high pressure.

It is another object of this invention to provide a design of dryercylinder which utilizes the maximum efficiency of steam and distributesthe heat uniformly over the exterior surface of the dryer cylinder. Bythis design, low pressure steam may be employed and a reduction incylinder weight is eiTected.

Further objects and advantages of this invention will become apparent inthe following detailed description thereof.

In the accompanying drawings,

Fig. 1 is a side elevation, partly sectioned vertically on the line I-lof Fig. 4, of a dryer cylinder embodying one form of my invention, thelower portion of the outer casing having been reremoved to disclose theunderlying shell.

Fig. 2 is an enlargement of the left half of Fig. 1 and showing-also thedetails of the bearing which is sectioned vertically.

Re erring to the drawings, I have disclosed a dryer cylinder whichembodies the principle of 'design constituting my invention. Instead oflling' the interior of the cylinder with a large mass of relativelystagnant steam vapor in which layers of air and water accumulate, Iprovide a dynamic, continuously moving. high-velocity stream of steam incontact with the interior surface of the cylinder, thus preventingaccumulation of insulating layers. For this purpose there is provided inaddition to the dryer or outer casing Il, an inner shell Il which ntsclosely within the casing. Passages following predetermined paths areformed between the adjacent surfaces of casing and shell, and steam athigh velocity is forced through the passages. The passages may be formedby cutting multiple'spiral grooves I2 in the outer surface of the shell,the ungrooved portions i5 remaining as lands or supporting surfaces forthe casing. The casing forms the remaining enclosing surface for thegrooves, thus constituting enclosed channels or passages. Each passageis formed with relatively large area and small depth, and the total areaoccupied by the passages constitutes a substantial portion o the area ofthe outer surface of shell and inner surface of casin'g I0. It will beapparent that steam blown through these passages is spread out and everyparticle of the vapor comes into intimate contact with the surroundingwalls of the channel, producing friction therewith.

The casing and shell may be closed at their ends by cylinder headsthrough which extend trunnions 2|, 2|' spaced apart by a hollow shaft22. The trunnions may be supported for rotation in suitable radial andthrust bearings 23 and 25 in bearing housings 26 and 21, and one of thetrunnions may have a sprocket, gear or pulley 2l fixed thereto wherebyrotation may be imparted to the casing and shell.

For delivering steam to the passages I2, there may be provided radialsteam pipes which connect with an axial steam delivery pipe 3| extendingthrough trunnion 2| and part way through the hollow shaft 22 from whichit is spaced to provide an annular passage 32. The inner end ofthe steamdelivery pipe is closed by a cap Il. The radial steam pipes extendthrough the wall of the shell and terminate in circular channels orpassages formed in' the exterior surface of the casing I0. Channels 40cut the spiral channels and thus serve to distribute the steam into themultiple spiral passages I2.

The discharge of the steam from the spiral pasmires 1s effect-.ed by apmmuty of radially drilled holes 46 leading into the interior of theshell. The holes may be disposed around the circum- -ference of theshell, substantially at the center and adjacent the ends thereof.

The path of the steam may be traced as entering through the hollowtrunnion 2| through the steam delivery pipe 3|, thence by way of radialsteam pipes 20 to the circular distribution passages 40. From passages40 the steam enters the multiplicity of spiral passages in which ittravels at high velocity. The steam nows in a thin layer equal to theshallow depth of the spiral channel. The steam is thus spread out andevery particle of the gas comes into intimate 'contact with thesurrounding metal walls of the channel,

in the spiral grooves until it reaches radial holes It where the steam,condensed vapor and any air carried along with the steam will dischargeinto the interior of the shell. Thus the channels are seavenged of airand water, and it is not possible to build up insulating layers. Theseare all conditions conducive to rapid heat transmission. Because of theabsence of insulating films there is no need for a high temperaturedifference to urge the flow of heat through the casing wall.Consequently, there is `no need to resort to high pressure steam.Instead of 40 lbs/sq. in. now usedA in some paper dryers, I find that 51bs./Sq. in. is ample to maintain circulation. This low pressure permitsthe use of a. very thin walled casing l0. This again accelerates heatflow. By employing low pressure steam, there is also gained theadvantage of having a greater quantity of heat available because thelatent heat of condensation is appreciably higher in the low pressuresteam than it is in high pressurelsteam; approximately 5% more in 5lbs/sq. in. than in 40l lbs/sq. in.

Vapor, water ofv condensation-andair accumullate in the interior ofshell Il. The interior surface of the shell is formed as a series of Vsarranged axially. Due to the centrifugal force of rotation, the ywaterwill flow into the bottom of the Vs from which points the water isevacuated through water discharge pipes 50. Each pipe 5|! extends' in aplane perpendicular to the exis of rotation, with its open inner endnear the bottom of the respective V while its outer end extends throughthe hollow shaft 22 to open into the an nular passage 32 between thesteam delivery pipe 3| and the hollow shaft. Each pipe 50 (see Fig. 4)is curved in a direction opposite to that of centrifugal impeller bladesto facilitate discharge towards the axis of rotation. The passage 32 isclosed at the end where the steam delivery pipe enters but opens intothe hollow passage through trunnion 2 Condensed water and air will thusbe blown out by the residual pressure in the interior of the shell, orthe now may be assisted by vacuum.

The foregoing description of the invention is merely illustrative andchanges may be made within the scope of the appended claims.

Having described my invention, what I claim and desire to secure byLetters Patent is:

i. A'rotatable dryer comprising a shaft having a passage therein, acylindrical outer casing mounted on the shaft, an inner shell, a spiralgroove between the casing and the shell, an annular groove intersectingthe spiral groove, an outlet connecting the spiral groove with theinterior of the inner shell, and at least one pipe connecting thepassage with the ,annular groove for delivering a continuous stream ofsteam under pressure to the annular groove for flow through the spiralgroove and the outlet at relatively high velocity.

2. A dryer as specied in claim 1, in which the outlet opening deliversthe discharged steam and entrapped air into the interior of the shelland the inner surface of the inner shell is formed with a plurality ofcollector grooves along the length thereof for collecting the condensedsteam.

3. A dryer as specified in claim 2, in which a drain pipe extends intoeach collector groove to a point adjacent the bottom thereof.

4. A dryer as specified in claim 3, in which a plurality of outlets arecircularly arranged adjacent the ends of the shell and intermediate theends. producing friction therewith The steam travels 76 5. A rotatabledryer comprising a shaft having a steam passage therein, a cylindricalouter casy ing mounted on the shaft, an inner shell in close contactwith the inner surface of the casing and provided with multiple spiralgrooves in the outer surface of the shell to form spiral passagewaysbetween the inner shell and the casing, an annu- ,lar grooveintersecting the spiral grooves to provide spiral passageways onopposite sides of the annular groove, outlet openings extending from thespiral grooves inwardly through the inner shell at points remote fromthe annular groove, and at least one passage connecting the steampassage with the annular groove for delivering a continuous stream ofsteam under pressure to the annular groove to force the steam inopposite directions through the spiral grooves on opposite sides of theannular groove.

6. A drying roll comprising a shaft having a steam passage therein, ahollow rollhaving a cylindrical outer wall and end closures mounted onthe shaft, the wall having a plurality of shallow helical passagestherein adjacent to the outer surface of the wall, means connecting thesteam passage to the helical passages to deliversteam at high velocityalong the helical passages, means to discharge steam, condensate andgases from the helical passages into the interior of the roll at pointsremote from the connecting means, and conduit means extending into theinterior of the roll and terminating adjacent to the wall fordischarging the steam, condensate and gases from the interior of theroll.

WILLIAM MESSINGER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

